Patent U.S. Pat. No. 5,506,296 discloses hot-melt adhesives with improved thermal resistance consisting of moisture-crosslinkable components. This document discloses a hot-melt adhesive composition based on an EVA copolymer (a copolymer of ethylene and vinyl acetate) and on a polyisocyanate, the EVA copolymer being a copolymer having a melt flow index at 190° C. under a load of 2.16 kg of between 100 and 1000 g/10 min and containing, with respect to the weight of the said copolymer: 1) 60 to 90% ethylene; 2) 10 to 40% vinyl acetate; and 3) 5 to 20 meq OH of an unsaturated ethylene termonomer carrying at least one primary hydroxyl functional group per mole, the said composition containing substantially no free hydroxyl functional group. Admittedly, these adhesives have good thermal resistance but it is necessary to wait until the crosslinking has been completed and, in addition, the use of isocyanates may pose toxicity problems. Another drawback is also the pot life of these adhesives, before applying them, which may be greatly reduced if the composition is not protected from moisture.
Patent WO 01/62804 discloses thermally reversible polymers containing nitroxide functional groups. It relates to the preparation of branched or crosslinked resins by the heat treatment of a polymer in the presence of a polynitroxide and, if necessary, a free-radical initiator, so as to obtain a resin having the property of thermal reversibility. The starting polymer may be a rubber or a thermoplastic polymer. The resins obtained offer processing conditions similar to those of the starting polymers, while having improved mechanical properties.
Patent U.S. Pat. No. 5,049,626 discloses a polyamide block graft copolymer obtained by the reaction (i) of a backbone which is a terpolymer of ethylene, an alkyl acrylate or a vinyl ester, and carbon monoxide with (ii) a monoamine-terminated polyamide of mass {overscore (M)}n of between 600 and 10 000 and preferably between 600 and 4000. This copolymer may optionally be blended with a tackifying resin.
Patent GB 2 262 939 discloses a polyamide-block graft copolymer obtained by the reaction (i) of a backbone which is an ethylene/acrylic acid copolymer with (ii) a monoamine-terminated amorphous polyamide. This copolymer is used as it is to coat steel sheet.
Patent EP 1 036 817 discloses a polyamide-block graft copolymer obtained by the reaction (i) of a backbone which is a copolymer of ethylene, propylene and, optionally, another α-olefin on which maleic anhydride has been grafted with (ii) a polyamide of mass {overscore (M)}n of between 3000 and 30 000 and preferably between 5000 and 20 000. This copolymer is then dissolved in toluene and this solution is sprayed onto polypropylene sheets.
Patent JP 60184579 A1 describes a polyamide (nylon-6)-block graft copolymer obtained by the reaction (i) of a backbone which is an ethylene/vinyl ester copolymer onto which maleic anhydride has been grafted with (ii) a nylon-6. This copolymer is then blended with a tackifying resin.
Patent EP 455 412 discloses a polyamide (nylon-6)-block graft copolymer obtained by the reaction (i) of a backbone which is a terpolymer of ethylene, an alkyl acrylate and a monomer (m) capable of reacting with an amine functional group with (ii) a monoamine-terminated nylon-6 of mass {overscore (M)}n of between 1000 and 3000. An additional condition is that, after attaching the PA-6 to the backbone, there remains on the said backbone at least 0.02 mol of (m) which has not reacted per 100 g of backbone. Another condition is that the MFI (Melt Flow Index) of the terpolymer before grafting be greater than or equal to 500 (g/10 min at 190° C. under a load of 2.16 kg). The PA-6 grafts have a melting point of about 205° C. The MFI at 190° C. of this polyamide-block copolymer cannot be measured because of the very high viscosity—it is necessary to blend it with a plasticizer in order to make an adhesive therefrom.